1. Field of the Invention
The present invention relates to a waterproof structure of a junction box used for connection of electrical wiring harnesses. The structure has an improved performance in heat transfer and waterproofness.
2. Background Art
Conventionally, a junction box mounted in an engine room of an automobile vehicle has a waterproof structure to prevent invasion of water into the box during vehicle washing with water jet, running in a rain, etc. However, a completely closed housing is not preferable, since a drainage caused by a temperature difference between the inside and the outside of the box can not be discharged from the box to have an adverse effect on electrical parts in the box. Therefore, the junction box mounted in the engine room has a construction allowing discharge of an inside drainage of the box as well as waterproofness against invasion of external water.
FIGS. 5 and 6 show conventional ones of such junction boxes, which are disclosed in Japanese Utility Model Application Laid-open No. H-1-24952 or Japanese Patent Application Laid-open No. H-10-126921. FIG. 5 shows a junction box 40 having a simple construction for preventing water invasion. The construction includes a lower cover 41 having a bottom wall 41a formed with a drain hole 42, a base (not shown) supporting the lower cover 41, and a seat structure (not shown) in a vehicle side to receiving the base. The construction defines an air flow passage 43 providing a venturi cooperating with the drain hole 42. The air flow passage 43 extends substantially parallel to an advancing direction of the vehicle.
In the above-mentioned construction, air flows through the air flow passage 43 during running of the vehicle to generate a negative pressure near the drain hole 42 communicating with the air flow passage 43. This discharges a drainage puddle in the lower cover 41 and prevents invasion of external water into the lower cover 41.
FIG. 6 shows another conventional junction box 45 disclosed in Japanese Patent Application Laid-open No. H-10-126921. The junction box 45, which is shown upside-down, has a drain hole 47 to easily discharge an inner drainage. The drain hole 47 has a sectional area enough to prevent blocking due to an interfacial force of the drainage. Around the drain hole 47, there are provided a pair of ribs 48 each having a round forward end.
Each rib 48 is semi-circular and extends from each side of the drain hole 47 having a square section. The ribs 48 guide a drainage flowing along an inclined inner wall of the lower cover 46 to adequately discharge it.
Japanese Patent Application Laid-open No. H-11-215653 discloses further another junction box having a main housing formed with a drain hole. The drain hole is provided with a blocking member for absorbing water invaded from the outside. The blocking member is a sheet or a sponge having water absorption and air permeable functions. The blocking member is disposed to cover the drain hole. The junction box has a lower cover with an inclined bottom along which a drainage flows to gather around the drain hole so as to be absorbed in the blocking member. The absorbed water drops through the drain hole or dries up naturally. Meanwhile, when the junction box receives a jet water during washing of an associated vehicle, the blocking member absorbs or plashes the water, preventing invasion of the water into the lower cover.
Japanese Utility Model Application Laid-open No. S-63-131519 discloses further another junction box having a lower cover with a drain hole that is overlaid by a wall. Japanese Utility Model Application Laid-open No. H-1-167082 discloses further another junction box having a lower cover with a vent hole for transferring heat generated in the box, and the lower cover is provided with a baffle plate to prevent invasion of external water. Japanese Utility Model Application Laid-open No. H-3-34618 discloses further another junction box having a lower cover with a drain hole, and an additional cover with another drain hole is provided such that the latter drain hole is offset from the drain hole of the lower cover.
However, the conventional junction boxes discussed above have problems described below. The lower cover 41 of the first conventional junction box shown in FIG. 5 has no vent hole to transfer heat generated in the lower cover 41, so that a higher temperature in the lower cover has adverse effects on electrical parts in the box. A larger opening of the drain hole 42 will serve to transfer heat but is disadvantageous for waterproofness of the cover 41.
The second conventional junction box shown in FIG. 6 has the lower cover 46 formed with the drain hole 47 to discharge a drainage in the junction box 45. However, the drain hole 47 is not designed to prevent invasion of an external water, which may cause erosion of electric parts in the junction box or undesirable leak of electrical current due to invasion of the water. Like the first one, the lower cover 46 has no vent hole, and the drain hole does not serve to efficiently transfer heat generated in the lower cover 46 to disadvantageously cause a higher temperature in the lower cover 46.
The junction box disclosed in Japanese Utility Model Application Laid-open No. H-1-167082 intends to have waterproofness and ventilation functions. However, the junction box has an additional cover and the baffle plate perpendicular to each other, which defines a labyrinth to insufficiently vent a heated air in the junction box.